Are you losing weight? I'm deliberately trying to burn my toxic body fat (mercury poisoning from dental amalgams) and one of the effects is that I've found myself struggling for breath when realy I have very good lung function. My best guess is that the toxins I'm excreting are interfering with my oxygen or producing too much co2. I'm guessing here. It's to do with me burning fat anyway. As an experiment I deliberately consumed something high in sugar so as to go into carbohydrate burning mode instead of fat burning mode and the problem went away.

I've also recently suffered from some dizzyness / lightheadedness at the end of a hard ride too.

It's bust or bust through but not with total abandon.

Regards, AnthonyG